1,5-dinitronaphthalene is an intermediate in the production of 1,5-diaminonaphthalene, naphthalenediisocyanate-1,5 and various condensation polymers.
In practice, a crude mixture comprising 1,5-dinitronaphthalene, 1,8-dinitronaphthalene, 1-mononitronaphthalene and products of partial oxidation may be prepared by nitration of naphthalene with mixtures of sulfuric and nitric acid (DE-A-11 50 965).
But, the use of mixtures of sulfuric acid and nitric acid in the production of crude mixtures of dinitronaphthalenes creates a need for the setting up of expensive and ecologically hazardous units for processing of used acids and separate recovery of nitric and sulfuric acids.
There are a number of publications which deal with increasing the yield in 1,5-dinitronaphthalene production by the introduction of reagents and solvents into the nitrating mixtures (U.S. Pat. No. 3,221,062, DE-A-24 53 529, FR-A-22 08 398, DD-A-26541).
But, it is much more advantageous to use nitric acid as a single nitrating agent in practice in order to avoid expensive separation and recovery processes.
From U.S. Pat. No. 3,998,893 a process for the production of a crude dinitronaphthalene mixture using nitric acid is known. But mononitronaphthalene is used as a primary raw material in the process according to U.S. Pat. No. 3,998,893. In addition, U.S. Pat. No. 3,998,893 does not provide any information about the isomeric composition of the produced crude dinitronaphthalene mixture, about the yield of 1,5 dinitronaphthalene and about its separation from the crude dinitronaphthalene mixture.
The separation and purification of 1,5-dinitronaphthalene from the crude dinitronaphthalene mixture is an important process step in the production of 1,5-dinitronaphthalene. But, no simple method for the separation and purification is known from the literature. In FR-A-13 20 250, the use of dimethylformamide (DMFA) as a selective solvent-extractant for the separation of 1,5-dinitronaphthalene is disclosed.
But, the technological complexity of dimethylformamide (DMFA) recovery and relatively considerable residual solubility of 1,5-dinitronaphthalene in the extractant render this method unsuitable for a practical implementation.